"""

Many-to-one relationships that can be null

To define a many-to-one relationship that can have a null foreign key, use

``ForeignKey()`` with ``null=True`` .

"""

from django.db import models

class Reporter(models.Model):

    name = models.CharField(max_length=30)

class Article(models.Model):

    headline = models.CharField(max_length=100)

    reporter = models.ForeignKey(Reporter, models.SET_NULL, null=True)

    class Meta:

        ordering = ("headline",)

    def __str__(self):

        return self.headline

class Car(models.Model):

    make = models.CharField(max_length=100, null=True, unique=True)

class Driver(models.Model):

    car = models.ForeignKey(

        Car, models.SET_NULL, to_field="make", null=True, related_name="drivers"

    )